About This Model
This simulator uses a simplified conceptual model to illustrate how arc flash variables interact. It is not an IEEE 1584 calculator and must never be used for actual hazard analysis or PPE selection. The underlying heuristic is E ∝ Iarc1.08 × t × configuration multipliers / Dx, where the arcing-current fraction and the distance exponent x (≈1.65 at low voltage, ≈1.8 at medium voltage) blend continuously across the 600–1000 V transition. It captures general trends but does not reproduce IEEE 1584-2018 results. Electrode, enclosure, and equipment multipliers are conceptual scaling factors, not empirically derived coefficients. Protection feature toggles apply conceptual clearing-time reductions; the fastest applicable scheme governs.
Limitations: Three-phase AC only (no DC, no single-phase). No protective-device coordination model. No equipment-maintenance condition factor. No short-circuit study — uses user-entered values directly. No arc-in-a-box correction per IEEE 1584-2018. Assumes 60 Hz for all cycle-to-millisecond conversions. Does not model the IEEE 1584-2018 reduced-arcing-current check, where lower arcing current can lengthen clearing time and increase energy. For actual arc flash studies, use IEEE 1584-2018 with validated short-circuit analysis performed by a qualified engineer.
BEFORE (Baseline)
AFTER (With Mitigations)
💡 What Changed?
Enable protection features in the sidebar (Maintenance Mode / ARMS, ZSI, Differential Protection) to see how faster clearing reduces incident energy. The summary above updates in real time.
Typical 480V MCC
480V, 25kA fault, 18in, 30-cycle clearing (standard breaker). Demonstrates how slow clearing on a common MCC configuration can dominate the hazard.
High Fault Switchgear
480V, 65kA fault, 24in, 6-cycle clearing (fast breaker). Shows the effect of very high available fault current even with fast clearing.
208V Panelboard
208V, 10kA fault, 18in, 6-cycle clearing (fast breaker). Lower voltage and fast clearing — compare the relative effect of voltage vs. clearing time.
4160V Switchgear
4160V, 12kA fault, 36in, 12-cycle clearing (relay). Medium voltage with greater working distance — observe how distance moderates the hazard.
Worst Case — Long Clearing
480V, 40kA fault, 18in, 90-cycle clearing. Illustrates the extreme hazard when high fault current meets a slow-clearing protective device.
Arc Flash Fundamentals
What Is an Arc Flash?
An arc flash is a sudden release of electrical energy through the air when insulation or isolation between conductors fails. The resulting arc can reach temperatures of 35,000 °F — more than three times the surface temperature of the sun. The blast produces intense light, pressure waves, sound, and molten metal spray.
Key Variables
- Incident Energy (cal/cm²): The thermal energy per unit area at a given working distance. This is the number that determines PPE requirements and hazard classification.
- Available Fault Current: How much current the system can deliver to a fault. Higher fault current means more energy released per unit time.
- Clearing Time: How long the protective device takes to interrupt the fault. This is often the most controllable variable and has a direct, nearly linear effect on incident energy. Analyses commonly cap exposure at 2 seconds where a worker can self-extract.
- Working Distance: Distance from the arc source to the worker. Energy decreases with distance following an approximate power-law relationship (Dx, where x ranges from roughly 1 to 2 depending on equipment class and configuration).
- Arc Flash Boundary: The distance at which incident energy drops to 1.2 cal/cm² (onset of second-degree burn). Workers inside this boundary need appropriate PPE.
- Electrode Configuration: The geometry of conductors inside equipment affects how the arc behaves. Enclosed and horizontal configurations can produce several times the energy of open or vertical ones by focusing energy toward the worker.
PPE Selection Concepts
- Incident-Energy Analysis Method: Under NFPA 70E, when using the incident-energy analysis method, the worker selects arc-rated PPE with an arc rating equal to or greater than the calculated incident energy at the working distance.
- At or below 1.2 cal/cm²: At or below the arc-flash boundary threshold. Non-melting or untreated natural-fiber clothing may be acceptable per the employer's electrical safety program.
- 1.2–40 cal/cm²: Arc-rated clothing and PPE must be selected with an arc rating meeting or exceeding the calculated incident energy. Face, head, hand, and hearing protection are required as dictated by the task and energy level.
- Above 40 cal/cm²: Often treated as an energized-work red flag by many safety programs because blast pressure, equipment condition, human factors, and task risk may not be adequately addressed by clothing arc rating alone. Apply engineering controls, remote work, or de-energization where practical.
Common Misconceptions
Not necessarily. A 480V system with high fault current and slow clearing can produce very high incident energy. Voltage alone does not determine the hazard.
Arc flash events regularly occur at 208V and 480V. Low-voltage equipment is where most energized work happens, and slow clearing at low voltage can make the hazard severe.
PPE is the last line of defense, not the first. Engineering controls (faster clearing, current-limiting devices, remote operation) should always be prioritized over relying on PPE alone.
A breaker's clearing time varies with fault current level. At lower fault levels, breakers may ride the long-time delay curve, resulting in much higher incident energy than expected. This is also why IEEE 1584-2018 requires checking a reduced arcing current: less current can mean a slower trip and more energy.
Test Your Understanding
Question 1
Which variable has the most direct, nearly linear effect on incident energy?
Question 2
What is the arc flash boundary defined as?
Question 3
A worker stands 18 inches from a 480V panel with 25kA available fault current. A current-limiting fuse clears in 3 cycles instead of 30 cycles. What happens to incident energy?
Question 4
What does Zone-Selective Interlocking (ZSI) accomplish?
Question 5
When using the incident-energy analysis method, what minimum arc rating should the PPE have?